The paper presents the results of studying the regularities and distribution pattern of natural radionuclides (potassium-40, thorium-232), as well as the representatives of the uranium family (radium-226, polonium-210) and the technogenic isotope cesium-137 in different objects of the water ecosystem in the North-Western District of Moscow (bottom sediment, hydrobiota). Some radiation parameters of these objects (the total alpha- and beta-activities of the radionuclides, their specific effective activity are given. On the basis of the experimental findings, the authors have made an assessment of the radioecological situation in the water pool of the district examined.